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In October 2014 the Swedish military launched an extensive hunt for what was rumoured to be a damaged Russian submarine in the Stockholm archipelago. A month later officials confirmed that a vessel had been present but said they didn't know where it came from.

Thursday 16th October

- Swedish intelligence hears a distress call from a vessel in the Stockholm archipelago, according to the Svenska Dagbladet newspaper (SvD).

- Swedish military will neither confirm nor deny report.

Friday 17th October

- Two civilians report sightings of a foreign vessel near Stockholm at Kanholmfjärden and Nämdöfjärden.

- Sweden's Armed Forces deploy over 200 troops.

- The operation marks the largest domestic military effort for Sweden since the Cold War.

Swedish troops have been searching out at sea and on the land. Photo: TT

Saturday 18th October

- Sweden intercepts further communications between transmitters in Stockholm archipelago and Russian enclave of Kaliningrad.

- Jesper Tengroth, press officer for the Swedish military, says the search "will continue until we consider that we are done".

- Experts suggest the distress call may mean the vessel is a damaged sub.

Sunday 19th October

- The Swedish Armed Forces release a picture (below) taken by a Swedish civilian in Jungfrufjärden that morning.

- The man, who has remained anonymous, told the Aftonbladet newspaper: "It was definitely a submarine, I'm certain about it".

An enlarged look at the mystery sighting. Photo: TT

Monday 20th October

- Russia denies the craft is theirs and suggests it is Dutch.

- The Netherlands deny the craft is theirs.

- Swedish Armed Forces set up exclusion zone - no civilian flights under 900 metres in the area.